Affinity spaces refer to digital and geographical spaces in which learning can happen, and some of the largest affinity spaces dedicated to education are those that currently exist on Twitter. These spaces are public, largely unmoderated, and thriving, yet very little is known about them. This paper seeks to shed some light on these basic questions about Twitter-based affinity spaces by presenting descriptive data about the participants and their patterns of activity across 47 State Educational Twitter Hashtags, or SETHs. We examine over 580,000 tweets collected over six months and identify who is participating and their degree of activity. We conclude with directions for future research on SETHs (or related affinity spaces on Twitter) focused on participants’ individual characteristics, the structure of the affinity space, and the content of tweets.